Dry eye is a chronic disease that affects tears and the keratoconjunctive epithelium. Causes of dry eye can be classified into the following types: “reduced tear type”, which is represented by Sjogren's syndrome, and “rapid evaporation type”, which is representative by Meibomian gland dysfunction (hereinafter also referred to as “MGD”). In other words, it is useful to detect abnormality in the Meibomian glands for specifying a cause for the dry eye.
The Meibomian glands are sebaceous glands located in the eyelids. The Meibomian glands supply sebum (oily substance), which creates oil layers over the surface of tears, preventing excessive evaporation of tears. The Meibomian glands exist from 20 to 30 in number in each of the upper and lower eyelids.
Technique for observing the morphology of the Meibomian glands is known as meibography. Conventionally practiced meibography has been a method of observing the structure of the Meibomian glands by illuminating them through the skin. It is, however, an invasive examination because the probe used for emitting light touches directly the eyelid, causing the subject to feel a strong unpleasantness. In addition, because the tip of the probe is thin and only capable of illuminating a narrow area, it is not easy to observe all the Meibomian glands in the upper and lower eyelids. Furthermore, doctors are required of the mastery of handling the probe.
On the other hand, a new type of meibography device is suggested to take advantage of the light source used in a slit-lamp microscope (Refer to patent document 1). This device comprises a slit-lamp microscope that is equipped with a small-size infrared CCD camera and an infrared filter. According to this device, all the Meibomian glands in the upper and lower eyelids are readily observable with low invasiveness.